A wavelength division multiplexing network has started to be commercially introduced, in which a wavelength division multiplexing transmission technique in an optical fiber transmission technique is utilized, and a wavelength of an optical signal is associated with a send and receive node pair, so as to realize optical communications of multiple-points to multiple-points. As to such an optical wavelength division multiplexing network, a ring-shaped or meshed optical wavelength division multiplexing network is constructed by connecting optical route switching apparatuses called ROADM (Reconfigurable Optical Add Drop Multiplexer) or WXC (Wavelength Cross-connect) using optical fibers. A client signal of a client communication apparatus such as a router is connected to an optical route switching apparatus via an optical communication apparatus called optical transponder, the optical transponder having a function for converting a client signal to an optical signal suitable for transferring over the optical network, and for converting a received optical signal into a client signal. The optical route switching apparatus performs a series of processes such as wavelength division demultiplexing of wavelength division multiplexed optical signals, editing of the optical signals for each destination, and wavelength division multiplexing of the optical signals, so as to realize optical communications between arbitrary client communication apparatuses connected to the optical wavelength division multiplexing network. The optical signal in the optical wavelength division multiplexing network that is currently commercially introduced is placed on frequency grids defined in ITU-T, in which the interval between center frequencies of adjacent optical signals is constant, e.g., 100 GHz.
On the other hand, an elastic optical path network has been proposed for appropriately adjusting the center frequency interval between adjacent optical signals according to requirements of individual optical signals in order to accommodate, more efficiently, optical signals of different bands and optical signals of different transmission distances from the viewpoint of frequency use efficiency (for example, refer to patent documents 1 and 2, and non-patent documents 1 and 2).